[lworld] RFR: 8336779: [lworld] C2 compilations hits "what's left behind is null" assert in do_checkcast

[Tobias Hartmann]

We assert because we don't expect an `InlineTypeNode` after a `null_assert`. The fix is to simply replace it with null in the parsing map. Full fix to enable scalarization of null after `null_assert` will be done by [JDK-8284443](https://bugs.openjdk.org/browse/JDK-8284443) (as the ToDo in the code at line 2198 already mentions).

Best regards,
Tobias

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Commit messages:
 - Removed ToDo
 - 8336779: [lworld] C2 compilations hits "what's left behind is null" assert in do_checkcast

Changes: https://git.openjdk.org/valhalla/pull/1199/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1199&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336779
  Stats: 60 lines in 2 files changed: 60 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/valhalla/pull/1199.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1199/head:pull/1199

PR: https://git.openjdk.org/valhalla/pull/1199